Characterization of prototype highly-multiplexed, multi-chroic pixels for balloon-borne platforms (Conference Presentation)

Abstract

EBEX-IDS is a balloon-borne polarimeter designed to characterize the polarization of foregrounds and to detect the primordial gravity waves through their B-mode signature on the polarization of the cosmic microwave background (CMB). EBEX-IDS will operate 20,562 transition edge sensor (TES) bolometers distributed among 3,427 polarization sensitive sinuous antenna multichroic pixels (SAMP) to observe the CMB in 7 frequency bands between 150 and 360 GHz. In order to maximize the sensitivity of the telescope and take advantage of the lower power emission and absorption of the atmosphere at float, we decrease the average thermal conductance of the bolometers by a factor of 10 compared to ground-based telescopes and observe within higher frequency bands. We use a meandered design with thinner legs to reduce the thermal conductance. We present prototype pixels which improve the technology readiness for the use of SAMPs in balloon and satellite platforms. We fabricated and tested 150/250/320, 180/250/320 and 220/280/350 GHz SAMPs suitable for EBEX-IDS with specified average thermal conductance of 9 pW/K designed to absorb as little as 0.2 pW at 150 GHz. We report on the characterization of the average thermal conductance, the critical temperature and the time-constant of these pixels as well as the measurement of their noise and optical properties. We also report on the fabrication and testing of a new inductor-capacitor chip operated at 4 K to read out up to 105 bolometers with two wires using the frequency domain multiplexing ICE readout boards. This factor represents an increase of 60% compared to the highest factor used to date with this readout system.